Many different ways of stimulating gastro-intestinal function have been explored, including pharmacological, neural, purely electrical, and combined methods. In particular, gastric electrical stimulation has been a subject of research investigation for many years (Bellahsene, B. E., C. D. Lind, B. D. Schirmer, O. L. Updike, and R. W. McCallum, "Acceleration of gastric emptying with electrical stimulation in a canine model of gastroparesis" Am. J. Physiol. 262(5 Pt 1):G826-34, 1992; Berger, T., J. Kewenter, and N. G. Kock, "Response to Gastrointestinal Pacing: Antral, Duodenal and Jejunal Motility in Control and Postoperative Patients" Annals of Surgery 164:139-44, 1965; Chen, J. D., B. D. Schirmer, and R. W. McCallum "Serosal and cutaneous recordings of gastric myoelectrical activity in patients with gastroparesis" Am. J. Physiol. 266(1 Pt 1):G90-8, 1994; Daniel, E. E. and S. K. Sarna "Distribution of Excitory Vagal Fibers in Canine Wall to Control Motility" Gastroenterology 71:608-13, 1976; Familoni, B. O., T. L. Abell, G. Voeller, A. Salem, O. Gaber, and D. Nemoto "Long-term electrical stimulation of the human stomach" Gastroenterology 106(2):A496, 1994; Sarna, S. K., K. L. Bowes, and E. E. Daniel "Gastric Pacemakers" Gastroenterology 70:226-31, 1976).
It is now well known that gastric contractions are controlled by gastric electrical activity ("GEA") (Sarna et. al., 1976). Moreover, when contractions are present, their temporal and propagation organization is strongly related to the organization of GEA. Therefore, electrical stimulation of the stomach may have particular application to a condition known as gastroparesis, in which the stomach is incapable of grinding, mixing and transmitting the food to the duodenum, and to other conditions in which gastric emptying time is abnormally delayed (Bellahsene et. al., 1992; Chen et. al., 1994).
Recently, gastric electrical pacemaking has once again become a subject of intensive investigation (Eagon J C and Kelly K A "Effect of electrical stimulation on gastric electrical activity, motility and emptying" Neurogastroenterology & Motility. 7:3945, 1995; The GEMS Group "Electrical stimulation for the treatment of gastroparesis--preliminary report of a multicenter international trial" Gastroenterology, 110:A668, 1996; Chen J D Z, Lin Z Y, Schirmer B D, Williams R D, Ross B and McCallum R W "Effect of gastric pacing with optimal parameters on gastric emptying in patients with gastroparesis" In: Proceedings of XV Int. Symposium on Gastrointestinal Motility, p. 42, Rome, Italy, October 1995).
In 1963, Bilgutay et. al. (Bilgutay A M, Wingrove R, Griffin W O, Bonnabeau R C and Lillehei C W "Gastro-intestinal Pacing. A New Concept in the Treatment of Ileus" Ann. Surg., 158;338-43, 1963) described marked shortening of the duration of postoperative ileus in patients using neural electric gastric stimulation ("NEGS") with a single antral intraluminal electrode and a single cutaneous reference electrode. However, subsequent well-controlled studies have failed to confirm a significant effect of NEGS on antral contractions or postoperative ileus.
Later studies have focused upon Electrical Control Activity ("ECA") entrainment, termed Gastric Electrical Pacing by Sarna et. al., 1976. Distal antral stimulation in dogs produced a delay in emptying of liquids and solids. Proximal stimulation to entrain ECA to a higher frequency was found to have no effect on antral emptying. These findings were confirmed by Kelly K A, and Code C F "Duodenal-gastric reflux and slowed gastric emptying by electrical pacing of the canine duodenal pacesetter potential" Gastroenterol., 72:429, 1977. Kelly et. al., 1977 demonstrated retrograde propulsion of duodenal contents with distal duodenal stimulation and entrainment of the duodenal pacesetter potential.
J. C. Eagon et. al., 1995 studied carefully the effects of low-frequency (0-20 Hz) electrical stimulation on canine gastric electrical activity (GEA), motility and emptying and concluded that although an increment of GEA frequency was observed when stimulating at 6 and 30 cycles-per-minute (cpm), gastric contractions and emptying were not affected by stimulation in the low frequency range. More optimistic findings were reported by The GEMS Study Group, 1996 in improvement of nausea and vomiting in humans, but no dramatic change in gastric emptying was evident.
Chen et al., October 1995, described slight acceleration of gastric emptying in a pilot study of a small number of patients with gastroparesis by performing GEP at one site on the greater curvature of the stomach and entraining ECA to a frequency 10% higher than the electrophysiological or basal. However, Bellahsene et. al., 1992, in a canine model of gastroparesis, failed to show any effect from GEP.
The within invention specifically utilizes a mathematical or computer model of gastric stimulation in order to derive the parameters of the electrical stimuli required to produce artificially propagated contractions in the stomach.
Mirrizzi et. al., 1985 (Mirrizzi N., R. Stella, U. Scafoglieri "A model of extra cellular wave shape of the gastric electrical activity" Med. Biol. Eng. & Comput, 23:33-37, 1985) and Mirrizzi et. al., 1986 (Mirrizzi N., R. Stella, U. Scafoglieri "Model to stimulate the gastric electrical control activity on the stomach wall and on abdominal surface" Med. Biol. Eng. & Comput, 24:157-163, 1986) suggest a conical dipole model of gastric electrical activity. The gastric electrical field was considered to be a result of electrical dipoles pointing towards the centre of the stomach in an approximately 2 mm. wide ring of depolarized smooth muscle cells. The conical dipole model assumes that the first such ring originates in the mid-corpus. With the continuous repolarization of the proximal layer of cells in the ring and the depolarization of the distal layer, the ring can be thought of as a dynamic entity that moves with an increasing velocity towards the pylorus, thus representing the dynamics of the depolarization-repolarization phenomena that take place in a healthy stomach.
However, a recent study by the inventors of the within invention (Mintchev, M. P. and K. L. Bowes "Conoidal Dipole Model of the Electrical Field Produced by the Human Stomach" Med. Biol. Eng. & Comput. 33:179-85, 1995) suggested a conoidal dipole model of gastric electric field (the "conoidal model") as an improvement over the previously known conical dipole model. In the conoidal model, as described in detail in Mintchev et. al., 1995, the area S of a d-wide ring of depolarized cells represented as dipoles pointing toward the center was given with: EQU S=2.pi..delta.r(t) Equation [1]
where r(t) represented the radii of the circles that build up this ring of dipoles. On the other hand, the relationship between the vector of the dipole density D and the vector of the equivalent dipole moment P (which is directly related to the number of depolarized cells in the ring and their depolarization level) is given with: EQU D=P/S Equation [2]
The articles by Mirrizzi et al., 1985 and 1986, set out above, suggested that .vertline.P.vertline. could be considered constant and estimated its value to be 2.2.times.10.sup.-6 C.m. They assumed that the charge distribution on each side of a given polarized cell in the ring is approximately equal, and the number or polarized cells in the ring remains the same, while the density of the cells increases in distal direction with the decrement of S. When considering gastric stimulation in the conoidal model, this assumption is deviated from and .vertline.P.vertline. is considered to be a variable. In fact, it is believed, and the conoidal model assumes, that changes in gastric electrical activity (GEA) associated with contractions cause the amplitude of this vector to fluctuate. However, these fluctuations could very well be obscured when the vector distance r between the point of interest and the infinitesimal area segment dS located on the ring of depolarized cells is sufficiently great (e.g. in electrogastrography): ##EQU1##
Although the conoidal model and equation [3] relate to the spontaneous GEA of a normal stomach (as is discussed further below), it is believed that the conoidal model may be able to reconstruct the temporal and propagation organization of the missing contractions in a gastroparetic stomach.
There is therefore a need for a method and a device for the electrical stimulation of smooth muscle comprising a portion of the gastrointestinal tract in order to facilitate or aid at least a partial emptying of such portion. Further, there is a need for a method and a device for the electrical stimulation of the smooth muscle of the stomach. Finally, there is a need for a method and a device which utilize the conoidal model to derive the parameters of the electrical stimulus required to produce artificially propagated contractions in the stomach sufficient to facilitate at least a partial emptying of the stomach.